Posted
by
Soulskill
on Saturday February 21, 2009 @11:20AM
from the rocket-fuel-green-cheese-hybrid dept.

Iddo Genuth writes "Pratt & Whitney Rocketdyne of West Palm Beach, Florida has successfully completed the third round of its Common Extensible Cryogenic Engine (CECE) testing for the National Aeronautics and Space Administration (NASA). CECE is a new deep throttling engine designed to reduce thrust and allow a spacecraft to land gently on the moon, Mars, or some other non-terrestrial surface."
NASA is also set to launch a new satellite on Tuesday — the Orbital Carbon Observatory — that will monitor the level of carbon dioxide in the atmosphere. On the research front, NASA has announced this year's Centennial Challenges. $2 million in prizes are available for a major breakthrough in tether strength (one of the major obstacles for developing a space elevator), and another $2 million is being offered to competitors who are able to beam power to a device climbing a cable at a height of up to one kilometer.

Another $2 million is being offered to competitors who are able to beam power to a device climbing a cable at a height of up to one kilometer.

Wouldn't it just make more sense to have solar panels in orbit and transmit the power along the space elevator? If I remember correctly, this is what Kim Stanley Robinson envisioned with the space elevator in his science fiction novel Red Mars [amazon.com] . Being able to bring power down would be a nice bonus for a tool to get up to orbit easily.

Depending on whether transmission along the cable is possible, a power source internal to the elevator car may be necessary. Though, it would seem that an internal power source is very undesirable. If cargo capacity and reduction of wear on the cable are important parameters for the elevator, then reducing on board weight for the car would indicate that an important goal is to try to find a method of powering the car externally.

i would guess that the power output is too small to overcome gravitynuclear batteries on probes have a very small output, barely enough for the onboard electronics.Nuclear subs on the other hand are immense and heavy.And nuclear subs have a much better temperature gradient to work with, since they have an infinite supply of water for cooling.

He casts-off RTGs immediately because their power output sucks, and then he dismisses naval fission reactors [fas.org] because (1) they're huge and (2) you need a way to remove the waste heat.

Unfortunately, efficiently creating mechanical/electrical energy from heat requires a large temperature differential. Once you've used-up all the energy you can and the temperature drops, the remaining energy is waste heat, and must be removed from the system. Naval r

Did you even READ the link I posted? The smallest reactor core on that page has a volume over 32,000 cubic feet, and weighs 1130 tons. 1130 TONS. That's one gigantic dustbin.

And keep in mind, these are some of the world's most advanced reactor designs. While the civilian nuclear power industry has largely langushed in the last 30 years, the military has been running a tight ship. You really can't make them any smaller with

...was reading just the other day about this company that proposes to put up solar panels in orbit and beam the energy down via microwaves. Now there was an image of an antenna farm on the earth below, implying you need a large collector area for this to work. However, the energy could be tight-beamed via a maser to a small antenna, perhaps - a small, light antenna mounted on the climber.

Microwaves aren't easily aimed. A maser is a very different type of device to an optical laser, the only similarity is that they both give coherent radiation. Lenses for microwaves aren't practical and the emitters aren't inherently directional as lasers are. The reason why the space power satellite would have needed such a giant field of rectennas is that at >100km range, getting more than 50% of the beamed power into a patch of less than a kilometre is next to impossible.

Apart from the really obvious one of needing an almost infinitely strong piece of cable? So far, carbon nanotubes (the main contender to make a very strong cable) are limited to being only a few millimeters long. Not quite the several kilometers they require for a space elevator.

I think one of the silliest notions I ever heard is the idea that we could propel a carriage without a horse, by using explosions from a highly explosive liquid substance. Obviously the first time they try this they are just going to blow the carriage sky heigh. The simple reason this will never work is that they forgot that a carriage has a thing called inertia, and it will quickly buckle under the force of the explosions rather than be propelled down the lane. Even if it could withstand the force of the explosions, could you imagine what kind of jerky ride you would have?

Why should it make more sense to not bother? Even if a space tether from Earth proves to be too difficult to bother with this century, we currently have the materials to make less ambitious tether strutures in orbit or a space elevator on the Moon.

Yes and no. Yes, by itself the moon's slow rotation would call for a really long tether (to match the 27.3 day rotational period, and the counterweight would be too strongly influenced by Earth's gravity. I haven't done the calculations, but it wouldn't surprise me if the tether would have to pass through the Earth itself.

However, there is another space elevator design that will work. Between the Earth and the Moon lies the first Lagrange poin

Apparently we have sufficiently strong materials right now to be able to create such a tether. There are still engineering difficulties (such as getting a 56,000+ km length of kevlar rope strung out from the moon to the counterweight) but a lunar tether lies within our current technological capabilites

The problem is that we don't actually need a lunar tether until we have one attached to Earth.

I would think that at some relatively low altitude it becomes more efficient to beam the power down just because you don't have to go through so much atmosphere.

For sheer impracticality, space elevator is one of the silliest ideas ever.

The Big Orbital Hand In The Sky (BOHITS) drops the Space Yo-yo and it spins as the nanotube tether unravels, since the other end of the tether is attached to the Big Middle Finger In The Sky. When it is just a few feet above the Earth, at the end of the tether, the clutch pulls away from the axle, and it spins, while the ground crew load up the non-spinning cargo core. Then the Big Middle Finger In The Sky jerks the tether, causing the clutch to grab the axle again, and the spinning of the Space Yo-yo cli

The Earth's atmosphere doesn't reduce the intensity of sunlight that much that we need to put solar panels in orbit.

Solar power stations in orbit don't require as many resources as the same stations on the ground (very large mirrors can be thin and light in microgravity, etc) and produce their full power output nearly 100% of the time, tracking the sun 24/7 and only rarely going into the Earth's shadow. They also don't take up a huge amount of space on the ground which could be used for other things, like growing crops.

That's not to say that they would be cost-effective, but there are good reasons for preferring space-ba

As someone who has worked in high power engineering, I will note that is easier said than done. Its really hard to send power a long distance efficiently even when you have lots of transformer stations and such along the way, and with the benefits of the ground plane and other factors you get in land based transmission systems. I just don't think it would be practical to send that much electrical power 1 km with modern affordable technology in a straight shot, even on Earth.

would be cool if somehow a superconductor transmission line could be incorporated into the space elevator (weight issues a prob). Or have it conducted on the surface (didn't NASA look at power generation from a tethered cable?) of the elevator cable. I'm not a EE so please forgive any ignorance.

talking of space elevators (slight offtopic, but still - funnily - related to the subject), couldn't we just use a counter-weight like a small asteroid or a roaming satellite to "lift" the elevator's cabin, like in traditional ones ?

Sounds good, though you have this problem of the original elevator is (currently well outside) at the limits of material strength over such a long distance --- AFAIK the weight to strength ratio limits the size of our current buildings to only a little larger than the Kuala Lumpur building as compared to the distance to build an effective space elevator. Our buildings do rely on compressive strength rather than tension that a space elevator type buildings would use.

Actually, it makes the most sense (to me) not to use a powered 'climber' at all.

If the space elevator is ever deployed, instead of dropping a single tether down to Earth, they should drop a LOOP. Run the bottom of the loop around a pulley on Earth, and the top through a pulley on the counterweight in space. Add a motor to the pulley on Earth and you've got one half constantly going up, and the other half constantly going down.

All a 'climber' would then have to do is clamp onto the cable and allow itself to

Well, there is the engineering challenge of making the elevator "cable" material sufficiently flexible that it can run through a pulley. A better approach would be to form the "cable" into a giant circle, and rotate the circle like a giant ferris wheel. Sounds silly, but if we're going to postulate a 100km load-bearing cable elevator, a 314km cable circle is equally feasible.

My idea of a pulley was something about 50 to 100 meters in diameter, much like a ferris wheel. It had less to do with flexibility though, and more to do with reducing wear and tear on the 'tether loop', preferrably bending it through a large radius, and exposing it to a large surface area for traction to drive it.

The only engineering challenge I can think of would be preventing the up-going side from touching, or coming too near the down-going side. Potentially solved with two pulleys each on the ground and in space, each pair a kilometer or more apart so the 'tether' goes down, across, and then back up.

You missed:

The shock loads of clamping and unclamping the 'climber' on both the cable and the climber.

The mechanical requirements for a gondola ride have been worked out already (e.g., http://en.wikipedia.org/wiki/Skyway_(Disney) [wikipedia.org]). Turning the cable into a loop is a clever idea that provides a route down as well as up, for instance.

As somebody else said, even if such a technology never proves practical on Earth, it certainly might be on other planets. Mars would be easier, for instance - less gravity, similar orbital period, thinner atmosphere.

Checking my math - it's hooey, of course. A lunar synchronous orbit is only a little more than twice the radius of a geosynchronous orbit. If we can build a cable 42,000 km long, we can build one 88,000 km in a lower gravity field and moving slower. Of course, if two guys can fly into lunar orbit using nothing but a single stage LEM, it isn't obvious we need a space elevator on the Moon.

The numbers for Mars might be the right trade-off. A synchronous orbit on Mars has less than half the radius as on Ear

It's not just about the route down, or the method of supplying potential energy to the payload. It's also about redundancy. If a tether breaks, you're out one counterweight and a lot of tether.

If a looped tether breaks, you simply put the brakes on at all four pulleys and you've still got a plain single tether. Send one bot up and one bot down the tether with the other 'half' of the tether looped over them, they clamp hard to the ends of the tether when reached, attach themselves together, and the looped te

Wouldn't it just make more sense to have solar panels in orbit and transmit the power along the space elevator?

I imagine it might add too much weight or complexity. Even just running two strips of conductive tether separated by an insulator may be too much considering how feasible the tether is to begin with. Then there are things such as resistance to consider. Might simply be easier to beam it seperatly rather than add another layer of complexity to something that is already pushing the limits.

All you need for the "space elevator" to work is a massive cable with one end anchored to an orbital, the other on Earth. The idea of it is to use an elevator to move materials from the surface into space.

To build a really decent power station in space, you're going to need to move a lot of materials from the surface up into orbit. Presumably the cheapest way to do this is to use your newly built space elevator- but you're going to need to pow

Except that recently the space elevator was deemed "impossible" because even with nanotubes of carbon molecules there would be too much constant structural damage. Hey, I was bummed out too.
Sorry, don't have the link handy. It had to do with japanese researchers.

Wouldn't it just make more sense to have solar panels in orbit and transmit the power along the space elevator?

Solar panels are great for powering electronics, which only need to move electrons, and small servos, which don't use much power. To lift payloads, I'm afraid sunlight is just too diffuse to do the job.

A large metal wire cutting through the earths magnetic field is all you need to generate electricity (ask anyone who plays the electric guitar). All you need to do is find a way to harness the current that would be generated in the space elevator cable.

If you attempted to stick a current through the elevator cable, my primitive understanding of physics says, oscillations will start to occur in the cable due to the way magnetism and electricity are related?

It's a step toward the soixante-neuf drive used by the ship Hwang Ho in Philip Jose Farmer's (under the peudonym of Kilgore Trout) "Venus on the Half Shell". So named because it could achieve 69000 times the speed of light, obviously.

We have worked on star wars programs....Is it not possible to build a super precise Laser based weapon to target the terrorists no matter where they are? A small pulse of Laser in the head of terrorist and he is gone. A good telescope with good precision laser should be able to take care of any terrorist without launching any drone attacks. I understand it may have its own technical challenges, but US certainly can do it. Isn't it?

My question is, though, how do you stay off the terrorist/person of interest/'enemy combatant'/etc list and still have some reasonable freedoms left? And how thick will the tinfoil need to be to keep that 15 MW laser from toasting your brains?

There are several reasons: 1) Gravity on Earth is high relative to these "non-terrestrial" surfaces. The CECE engine might not have the thrust/weight ratio to land on Earth. 2) Earth also has a thick atmosphere. That greatly reduces the throttling capability and you need to come up with a gimmick like thrust augmented nozzles [blogspot.com] to maintain nozzle efficiency (and ISP) in atmosphere. 3) There are other means of landing on Earth (eg, parachutes).

See... http://www.luft46.com/misc/sanger.html [luft46.com]
Note the engine details. There is a jet engine fuelled by liquid oxygen and hydrogen, piped through the jet bell, so it gets cooled and the fuel gets vapourized.
Neat, eh? Clever guys, those Germans.